Inorganic powders, such as fumed silica, are used as thickeners, thixotropics, and reinforcing agents in materials such as inks, resins, rubber, paints and cosmetics. More particularly, they are used to modify the properties, such as the physical, mechanical and thermal properties, of a variety of plastic and elastomeric products such as silicone rubbers.
Inorganic powders are also used as sorbents as disclosed in U.S. Pat. No. 5,037,557. For example, inorganic powders can be used to absorb hydrocarbons, such as oil, from water. Silica is one of the inorganic powders which is used as a sorbent for organic compounds. This requires the silica, which has untreated hydrophilic hydroxy groups on its surface, to be treated with a silylating agent to render it hydrophilic.
In recent times the chemical industry has been adhering to stringent emission requirements for new and existing plants. However, it is increasingly becoming more challenging, especially when by-products of a chemical processes have low melting points and high vapor pressures at ambient conditions. Illustrative examples of such by-products are organosilicon materials such as hexamethyldisilazane (HMDZ), hexamethyldisiloxane (MM), and trimethylsilanol (TMSOH).
The current technology uses a non-condensable gas, such as nitrogen, to convey and strip undesired volatile by-products from the chemical processes. New emission standards, for example, which limit the emission of mole fraction of MM to 0.004 mole/h, based on a plant running 123 Kg/h of nitrogen, is very stringent, considering the physical properties of MM. Conventional condenser technology does not help meet these stringent emission requirements. There is thus a need for an efficient process that will help isolate residual volatiles from silica treatment processes. Grinberg et al., in the Russ. J. of Chem. 60 (5) 779 (1986) report experimental values indicated a MM vapor pressure of 17.5 mm of Hg at 7.degree. C. using the conventional condenser technology. The vapor pressure value indicates an emission of MM which is greater than the 0.004 mole/h, as required by the new emission standards.
It has been surprisingly found that the process of the present invention provides an efficient and effective method for isolating residual volatiles from a silica treatment process. The process of the present invention uses condensable gas, namely, steam, to convey (transport) and strip residual volatiles from a silica treatment process. The present invention is not restricted to a silica treatment process, and can be used to remove volatile by-products from other inorganic processes.